This invention generally relates to an impact energy absorbing apparatus in the form of two telescoped cylindrical members subject to axial impact, and more particularly to an improved steering column assembly for use in vehicles.
With the latest tendency toward ever increasing speed-up of motor vehicles the problem of safeguarding a vehicle driver against collision accidents has become more and more serious. On the occasion of collision, the driver bends forward due to inertia to strike his breast against the manual steering wheel thus being wounded seriously or otherwise. In this view, therefore, it has been conventional to arrange in the vehicle steering column assembly that both of an inner steering shaft assembly connected to the manual steering wheel and an outer supporting mast jacket or cylindrical post assembly be adapted for telescopic movement in the axial direction for absorption of shock energy axially applied thereto. As is commonly known, the most typical design is that the outer supporting post assembly is made up of two post sections adapted for telescopic engagement with each other with shock absorbing elements interposed therebetween. For example, an impact energy absorbing apparatus disclosed in a Japenese Patent Serial No. 35527/71 employs rolling spherical elements or rigid balls press-fitted in and between two telescopically engaged posts so that when the posts effect axial relative movement under impact applied thereto, the rigid balls cause localized plastic deformation of the wall surfaces of the posts along their rolling paths.
However, such prior art impact absorbing apparatus still has had difficulty with respect of securing a full extent of safeguard against collision accidents. Namely, when the outer supporting post of the steering column assembly starts its movement of telescopic contraction under an impact load axially forwardly applied thereto, or at the time of the steering column assembly commencing its shock absorbing stroke, there generally will occur a significantly high magnitude of initial load that in addition to a load to the impact absorbing elements of rigid balls, includes those to rupture shear pins ordinarily used in a steering shaft, a breakaway bracket capsule, etc., a load of inertia due to moving masses, and other possible loads. To hold down this high magnitude of initial load, therefore, the shock absorbing characteristic of the apparatus has to be lowered so that further loads to be absorbed by the apparatus will be abruptly decreased. Thus, the efficiency of impact absorption attainable is deteriorated.